Dendritic cells and lipidomics in asthma

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Allergic asthma, which shows increasing prevalence, is characterised by chronic inflammation and smooth muscle hyper-reactivity of airways, symptoms probably induced by excessive T-helper cell type 2 responses to normally benign inhaled antigens. There is a changed eicosenoid production and involvement of dendritic antigen presenting cells (DC) in production of inflammatory lesions. Using in vitro studies, we showed that lipid bodies - known to be sites of eicosanoid metabolism - appear in DC influenced by certain fatty acids, cytokines or antigenic exposure. We have also shown that, in vivo, the balance of fatty acids and hence availability of lipid mediator precursors differs between leukocytes, serum and adipose tissue. A major challenge in studying lipid-DC interactions in human inflammatory diseases such as asthma is the difficulty in sampling relevant tissues. By inducing sputum, a comparatively non-invasive technique, we were able to harvest human airways DC. In asthma, these DC showed a mature phenotype, increased capacity to endocytose antigen and increased expression of CD1 molecules.
We will investigate the hypothesis that changes in uptake and metabolism of fatty acids within DC alter signalling pathways, modulating DC functions instrumental in the development of asthma. In order to test this hypothesis we shall study DC from both sputum and peripheral blood and ask whether distribution of fatty acids and their metabolites in lymphocytes and DC are altered in asthma. The induction of lipid bodies and their molecular components will be studied using electron and confocal microscopy, flow cytometry and fatty acid/eicosenoid analysis to test whether they are sites of changed lipid mediator production in asthma. We shall then ask whether mechanisms of activation of DC via receptors involved in both immune activation and lipid metabolism, particularly PPARgamma, are changed in asthma and whether ex vivo airway DC from asthma patients show evidence of activation via these pathways using our sensitive quantitative gene expression technique in purified DC. Finally, in parallel we will investigate the role of upregulated CD1 on DC in asthma, by characterising the CD1-restricted responses of T- and NKT-cells, stimulated by DC, using 5- (and 6-) carboxyfluorescein diacetate succinimidyl ester (CFSE) labelling and multi-colour flow cytometry.
In conclusion, study of uptake and metabolism of fatty acids by DC will provide novel information about links between the roles of fatty acids and eicosanoids and the immune system in asthma and provide a sounder evidence-base for development of rational dietary and immunomodulatory therapies for asthma.